Composition for overcoat layer of organophotoreceptor, organophotoreceptor manufactured by employing the same and the electrophotographic imaging apparatus containing the same

ABSTRACT

A composition for an overcoat layer suitable for use in an organophotoreceptor for liquid toner, an organophotoreceptor manufactured by employing the composition and an electrophotographic imaging apparatus containing the organophotoreceptor. Since the organophotoreceptor can maintain higher charge potential and low residual or discharge potential, the lifetime of the organophotoreceptor can be extended. Also, since the organophotoreceptor has good solvent resistance and abrasion resistance, it can be advantageously used for liquid toner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending applicationSer. No. 10/681,324 filed Oct. 9, 2003, now pending, and claims thebenefit of Korean Patent Application No. 2002-61490, filed Oct. 9, 2002,in the Korean Intellectual Property Office, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composition for an overcoat layer ofan organophotoreceptor, an organophotoreceptor manufactured by employingthe same and an electrophotographic imaging apparatus containing thesame. More specifically, the invention relates to a composition for anovercoat layer suitable for use in an organophotoreceptor for liquidtoner, the composition having good electrical properties and increasedabrasion resistance and adhesion to extend the lifetime of anorganophotoreceptor. The present invention also relates to anorganophotoreceptor manufactured by employing the composition and anelectrophotographic imaging apparatus containing theorganophotoreceptor.

2. Description of the Related Art

In electrophotography, an organophotoreceptor has an electricallyinsulating photoconductive element on an electrically conductivesubstrate and may be in the form of a plate, disk, sheet, belt, drum orthe like. An electrophotographic imaging process using theorganophotoreceptor will now be described briefly.

First, the surface of an organophotoreceptor having an electricallyconductive substrate where a charge transport material and chargegenerating material are provided is electrostatically charged, and thenthe charged surface is imagewise exposed to light. The light exposureselectively dissipates the charge in illuminated areas, thereby forminga pattern of charged and uncharged areas. Finally, a toner is thendeposited on the surface to create a toner image on the surface of thesubstrate. The resulting toner image can be transferred to a suitablereceiving surface such as paper. The imaging process may be repeatedmany times.

Both single layer and multilayer photoconductive elements have beenused. In single layer embodiments, a charge transport material andcharge generating material are combined with a polymeric binder and thendeposited on the electrically conductive substrate. In multilayerembodiments, the charge transport material and charge generatingmaterial are in the form of separate layers, each of which canoptionally be combined with a polymeric binder, deposited on theelectrically conductive substrate. Two arrangements are possible. In onearrangement (the “dual layer” arrangement), the charge generating layeris deposited on the electrically conductive substrate and the chargetransport layer is deposited on top of the charge generating layer. Inan alternate arrangement (the “inverted dual layer” arrangement), theorder of the charge transport layer and charge generating layer isreversed.

In both the single and multilayer photoconductive elements, the purposeof the charge generating material is to generate charge carriers (i.e.,holes and/or electrons) upon exposure to light. The purpose of thecharge transport compound is to accept at least one type of these chargecarriers and transport them through the photosensitive layer in order tofacilitate discharge of a surface charge on the photoconductive element.

An organophotoreceptor may be easily worn due to friction between tonerand a roller or a cleaning blade, which decreases the thickness of theorganophotoreceptor, resulting in a reduction in lifetime. To overcomethis problem, an overcoat layer may be formed on theorganophotoreceptor.

In recent years, there has been an increase in the development ofelectrophotographic printers using liquid toners, making it is necessaryto develop organophotoreceptors for liquid toners. However, conventionalovercoat layers have been proposed to extend the lifetime of anorganophotoreceptor for dry toner. Therefore, there is still growingdemand for overcoat layers that can extend the lifetime of anorganophotoreceptor suitable for liquid toners, having improvedelectrical and mechanical properties.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided acomposition for an overcoat layer of an organophotoreceptor, which canimprove electrical, and mechanical properties as well as increase thelifetime of the organophotoreceptor suitable for liquid toner.

Additional aspects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

In an aspect of the present invention, there is provided a coatingcomposition for an overcoat layer of an organophotoreceptor comprisingpolyaminoether, an electron transport material and an alcoholic solvent.

The polyaminoether is preferably hydroxylated polyaminoether.

The polyaminoether is represented by the following formula, and iscontained in an amount of 70 to 99 parts by weight based on 100 parts byweight of the solid content of an overcoat layer:

wherein n is an integer from 10 to 400.

The electron transport material may contain an electron transportmaterial represented by the following formula:

wherein A and B are independently one selected from the group consistingof a hydrogen atom, a halogen atom, a C₂-C₃₀ substituted orunsubstituted alkoxycarbonyl group or a C₂-C₃₀ substituted orunsubstituted alkylaminocarbonyl group, and the hydrogen atom in thebenzene ring can be substituted by halogen atom(s).

Examples of the alcoholic solvents include, but are not limited to,1-methoxy-2-propanol, methanol, ethanol, propanol, butanol andisopropanol, and are contained in an amount of 70 to 99 parts by weightbased on 100 parts by weight of the coating composition for an overcoatlayer.

In another aspect of the present invention, there is provided anorganophotoreceptor comprising an electrically conductive substrate, aphotosensitive layer formed on the electrically conductive substrate,and an overcoat layer formed by coating the composition for an overcoatlayer on the photosensitive layer and drying.

The overcoat layer may have a thickness of 0.01 to 5 μm, and thephotosensitive layer may be a single layer having both a chargegenerating material and a charge transport material or a double layer inwhich a charge generating layer containing a charge generating materialand a charge transport layer containing a charge transport material arelaminated.

In still another aspect of the present invention, there is provided anelectrophotographic imaging apparatus comprising a plurality of supportrollers, and an organophotoreceptor operably coupled to the supportroller with motion of the support rollers resulting in motion of theorganophotoreceptor, wherein the organophotoreceptor comprises anelectrically conductive substrate, a photosensitive layer formed on theelectrically conductive substrate, and an overcoat layer formed bycoating the composition for an overcoat layer on the photosensitivelayer and drying.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the invention will become apparent andmore readily appreciated from the following description f the preferredembodiments taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a diagram illustrating (not to scale) an organophotoreceptor.

FIG. 2 is a schematic representation of an electrophotographic imagingapparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the aspects of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout. The aspects are described below in order to explain thepresent invention by referring to the figures.

FIG. 1 is a diagram illustrating (not to scale) an organophotoreceptor 1comprising an electrically conductive substrate 2, a photosensitivelayer 3 formed on the electrically conductive substrate 2, and anovercoat layer 4 formed on the photosensitive layer 3.

A coating composition for an overcoat layer suitable for use in theorganophotoreceptor according to the present invention, wherein theorganophotoreceptor comprises an overcoat layer manufactured byemploying the composition and an electrophotographic imaging apparatususing the organophotoreceptor, will now be described in detail.

The present invention provides a coating composition for an overcoatlayer for an organophotoreceptor comprising polyaminoether, an electrontransport material and an alcoholic solvent.

The polyaminoether, a polymer having good oxygen permeation resistance,may be a hydroxylated polyaminoether, preferably, a compound representedby the following formula:

wherein n is an integer from 10 to 400, preferably 10 to 90.

Preferably, the polyaminoether represented by the above formula has aweight average molecular weight in the range of 4,000 to 160,000. If theweight average molecular weight of the polyaminoether represented by theabove formula is out of the range specified above, coating of thecomposition for an overcoat layer is difficult to achieve or solubilityof the alcoholic solvent is undesirably poor.

The electron transport material is exemplified by a compound representedby the following formula:

wherein A and B are independently one selected from the group consistingof a hydrogen atom, a halogen atom, a C₂˜C₃₀ substituted orunsubstituted alkoxycarbonyl group or a C₂˜C₃₀ substituted orunsubstituted alkylaminocarbonyl group, and the hydrogen atom in thebenzene ring is substitutable by halogen atom(s). The number of carbonatoms in the substituted or unsubstituted alkoxycarbonyl group or thesubstituted or unsubstituted alkylaminocarbonyl group is preferably inthe range of 2 to 15, more preferably 2 to 8.

The above compound may be exemplified by the following formulas:

The electron transport material that can be used for theorganophotoreceptor according to the present invention is not limited tothose stated herein and can be used alone or in a mixture of two or morekinds of those compounds.

The amount of the electron transport material may be in the range of 0.1to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100parts by weight of the solid content of an overcoat layer. If the amountof the electron transport material is less than 0.1 parts by weight, theelectron transporting capability of the overcoat layer decreases,deteriorating electrostatic properties of the organophotoreceptor. Ifthe amount of the electron transport material is greater than 50 partsby weight, abrasion resistance of the overcoat layer may be lowered orsolubility of the electron transport material may be undesirably poor.

The coating composition for an overcoat layer according to the presentinvention includes a solvent. Any solvent that can dissolvepolyaminoether can be used, and an alcoholic solvent is preferred.Examples of the solvent include at least one selected from the groupconsisting of 1-methoxy-2-propanol, methanol, ethanol, propanol, butanoland isopropanol. Preferably, 1-methoxy-2-propanol is used alone or amixed-solvent containing 1-methoxy-2-propanol and at least one alcoholicsolvent selected from the group consisting of methanol, ethanol, butanoland isopropanol, is used. The solvent is preferably contained in anamount of 70 to 99 parts by weight based on 100 parts by weight of thecoating composition for an overcoat layer. If the amount of the solventis less than 70 parts by weight, the overcoat layer is excessivelythick, and an exposure potential of the organophotoreceptor becomes highand a residual potential and an exposure potential sharply increaseduring charge-exposure-erase cycling. If the amount of the solvent isgreater than 99 parts by weight, the overcoat layer is overly thin,resulting in the deterioration of mechanical properties of the overcoatlayer, such that it may be easily worn. Also, if the amount of thesolvent is less than the range specified above, solubility of thesolvent is undesirably poor. If the amount of the solvent is greaterthan the range specified above, coating of the composition for anovercoat layer is difficult to achieve and the overcoat layer is toothin to function properly.

In the case of using the mixed-solvent consisting of1-methoxy-2-propanol and at least one alcoholic solvent, the alcoholicsolvent is preferably used in an amount of 1 to 30 parts by weight basedon 100 parts by weight of total content of 1-methoxy-2-propanol.

In another aspect of the present invention, there is provided anorganophotoreceptor having improved electrical, and mechanicalproperties as well as an increased lifetime by employing the overcoatlayer manufactured from the composition.

The organophotoreceptor according to the present invention includes anelectrically conductive substrate, a photosensitive layer formed on theelectrically conductive substrate, and an overcoat layer formed bycoating the composition for an overcoat layer on the photosensitivelayer and drying.

Preferably, the photosensitive layer includes a charge transport layerformed on the electrically conductive substrate and a charge generatinglayer formed on the charge transport layer.

The overcoat layer preferably has a thickness of 0.01 to 5 μm. If thethickness of the overcoat layer is less than 0.01 μm, the overcoat layeris not effective in protecting underlying layers. If the thickness ofthe overcoat layer is greater than 5 μm, electrical properties thereof,including an increased exposure potential, may undesirably deteriorate.

The photosensitive layer may have a single layer with both a chargetransport material and a charge generating material or may have a doublelayer in which a charge generating layer, containing a charge generatingmaterial, and a charge transport layer, containing a charge transportmaterial, are laminated.

A method of manufacturing an electrophotographic organophotoreceptorusing the composition for an overcoat layer according to the presentinvention will now be described.

A photosensitive layer is first formed on an electrically conductivesubstrate. Here, the photosensitive layer may be formed by sequentiallylaminating a charge transport layer containing a charge transportmaterial and a charge generating layer containing a charge generatingmaterial or laminating these layers vice-versa. Alternatively, asingle-layer photosensitive layer containing both a charge transportmaterial and a charge generating material may be formed.

The charge transport layer is formed by coating a composition comprisinga charge transport material, a binder and an organic solvent andthereafter drying the layer. The charge generating layer is formed bycoating a composition comprising a charge generating material, a binderand an organic solvent and thereafter drying the layer.

Examples of the charge transport material include, but are not limitedto, pyrazoline derivatives, fluorene derivatives, oxadiazolederivatives, stilbene derivatives, hydrazone derivatives, carbazolehydrazone derivatives, triaryl amines, polyvinyl carbazole, polyvinylpyrene, and polyacenaphthylene.

Examples of the charge generating material include, but are not limitedto, metal-free phthalocyanine (e.g., Progen 1×-form metal-freephthalocyanine, ZENECA INC.), and metal phthalocyanine such as titaniumphthalocyanine, copper phthalocyanine, titanyloxy phthalocyanine, orhydroxygallium phthalocyanine.

The charge transport material may be used in a generally acceptedamount, that is, in an amount of 35 to 65 parts by weight based on 100parts by weight of the composition for forming the charge transportlayer. The charge generating material may be used in an amount of 55 to85 parts by weight based on 100 parts by weight of the composition forforming the charge generating layer.

The binder may dissolve or disperse the charge transport material orcharge generating material, and examples thereof include, but are notlimited to, polyvinyl butyral, polycarbonate, poly(styrene-co-butadiene), modified acryl polymer, polyvinyl acetate,styrene-alkyd resin, soya-alkyl resin, polyvinyl chloride,polyvinylidene chloride, polyacrylonitrile, polyacrylic acid,polyacrylates, polymethacrylates, styrene-based polymers, alkyd resin,polyamides, polyurethanes, polyesters, polysulfones, polyethers andmixtures thereof. In the present invention, polycarbonate or polyvinylbutyral is preferably used. The binder is used in an amount of 15 to 65parts by weight, based on 100 parts by weight of the composition forforming the charge generating layer or the charge transport layer.

Examples of the organic solvent used for the charge transport layerforming composition or charge generating layer forming compositioninclude, but are not limited to, tetrahydrofuran, methylene chloride,chloroform, dichloroethane, trichloroethane, chlorobenzene, andacetate-based solvent. The amount of the organic solvent may be in arange of 70 to 99 parts by weight based on 100 parts by weight of thecomposition for forming the charge generating layer or the chargetransport layer.

The charge transport layer forming composition or the charge generatinglayer forming composition may be coated in accordance with anyappropriate technique known in the art without limitation. In the casewhere the electrically conductive substrate is a drum-like substrate,ring coating or dip coating is preferably used.

As described above, after the photosensitive layer is formed on theelectrically conductive substrate, the composition for an overcoat layeraccording to the present invention is coated on the photosensitive layerand dried, thereby completing the organophotoreceptor according to thepresent invention. The drying is performed at 80 to 140° C., preferablyat 100 to 130° C.

The composition for an overcoat layer may be coated by spin coating, dipcoating or ring coating. In the case where the electrically conductivesubstrate is a drum-like substrate, ring coating or dip coating ispreferably used.

In the organophotoreceptor according to the present invention, theoverall thickness of the photosensitive layer may be between 5.1 to 26μm. The thickness of the charge generating layer is in the range of 0.1to 10 μm, the thickness of the charge transport layer is in the range of5 to 25 μm, and the thickness of the electrically conductive substrate,in particular, the drum-like substrate, is generally in the range of 0.5to 2 mm. The overcoat layer has a thickness of 0.01 to 5 μm, asdescribed above.

The organophotoreceptor according to the present invention may furtherinclude additional layers. These additional layers are widely knownlayers, for example, a charge blocking layer. The charge blocking layermay inhibit charge infusion from the electrically conductive substrateto the photosensitive layer or may enhance adhesion between theelectrically conductive substrate and the photosensitive layer.

In the electrophotographic imaging process using theorganophotoreceptor, the toner can be either a dry toner or a liquidtoner.

If the conventional organophotoreceptor for dry toner is employed inelectrophotography using liquid toner, the organophotoreceptor contactsa paraffinic solvent, a component of liquid toner, resulting in crackingor crazing or partial elution of components of the organophotoreceptor.

On the other hand, since the organophotoreceptor according to thepresent invention is highly resistant to a paraffinic solvent, it can beused for an electrophotographic imaging process using liquid toner andthe various problems associated with the prior art can be avoided. Also,the organophotoreceptor according to the present invention exhibits goodabrasion resistance in the presence of liquid toner.

FIG. 2 is a schematic representation of an electrophotographic imagingapparatus 30. The electrophotographic imaging apparatus 30 includes anorganophotoreceptor unit. The organophotoreceptor unit generallyincludes a drum 28 that is attachable to and detachable from theelectrophotographic apparatus 30, and an organophotoreceptor 29 disposedon the drum 28. The imaging apparatus further includes a charging device25 which charges the organophotoreceptor unit, an imagewise lightirradiating device 22 which irradiates the charged organophotoreceptorunit with imagewise light to form an electrostatic latent image with atoner to form a toner image on the organophotoreceptor unit, and atransfer device 27, which transfers the toner image onto a receivingmaterial, such as paper P. The charging device 25 may be supplied with avoltage as a charging unit and may contact and charge theorganophotoreceptor 29. Where desired, the apparatus may also include apre-exposure unit 23 to erase residual charge on the surface of theorganophotoreceptor 29 to prepare for a next cycle. The imagingapparatus further includes an electrophotographic cartridge 21, adeveloping device 24 which develops an electrostatic latent image formedon the organophotoreceptor 29, and a cleaning device 26 which cleans asurface of the organophotoreceptor 29.

The electrophotographic imaging apparatus according to the presentinvention also comprises a plurality of support rollers (not shown), andan organophotoreceptor operably coupled to the support rollers wheremotion of the support rollers results in motion of theorganophotoreceptor. The organophotoreceptor comprises an electricallyconductive substrate, a photosensitive layer formed on the electricallyconductive substrate, and an overcoat layer formed by coating thecomposition for an overcoat layer on the photosensitive layer and dryingthe layer.

An electrophotographic imaging process using the organophotoreceptoraccording to the present invention will now be described.

First, the surface of an organophotoreceptor having an electricallyconductive substrate, where a charge transport material and a chargegenerating material are provided, is uniformly electrostaticallycharged, and thereafter the charged surface is imagewise exposed tolight. The light exposure selectively dissipates the charge inilluminated areas, thereby forming a pattern of charged and unchargedareas. Finally, a liquid or dry toner is deposited on the surface tocreate a toner image on the surface of the substrate. The resultingtoner image can be transferred to a suitable receiving surface such aspaper. The imaging process may be repeated many times.

The liquid toner is prepared by dispersing a colorant, a binder resin, acharge control agent and the like in a liquid carrier.

Examples of the liquid carrier include aliphatic hydrocarbons such asn-pentane, hexane or heptane, alicyclic hydrocarbons such ascyclopentane or cyclohexane, aromatic hydrocarbons such as benzene,toluene or xylene, halogenated aliphatic hydrocarbons such aschlorinated alkane, fluorinated alkane or chlorofluorocarbon, siliconoils or mixtures thereof. Specifically, aliphatic hydrocarbon solvents,in particular, paraffin solvent mixtures such as ISOPAR G, H, L, K, V orM, or NORPAR 12, 13, or 15 (Trade name) available from EXXON, arepreferably used. The amount of the solvent is 5 to 100 parts by weightbased on 1 part by weight of the colorant.

Useful colorants are well known in the art, and include materials suchas dyes, stains, and pigments. Examples of suitable colorants include,but are not limited to, phthalocyanine blue (C.I. PIGMENT BLUE),monoarylide yellow, diarylide yellow, arylamide yellow, azo red,quinacridones, magenta and black pigments, such as finely dividedcarbon, and the like.

Hereinafter, the present invention will be described in greater detailwith reference to the following examples. The following examples are forillustrative purposes and are not intended to limit the scope of theinvention.

EXAMPLE 1

A charge transport layer was formed as follows: 2 g of a hydrazone-basedcharge transport material (of the following formula synthesized fromU.S. Pat. No. 6,066,426), and 2 g of polycarbonate (PCZ200, MitsubishiChemical, Japan) were dissolved in 16 g of tetrahydrofuran (THF), thesolution was then filtered using a syringe filter having a pore size of1 μm, and coated on an aluminum drum at a speed of 300 mm/min using aring coater, giving a charge transport layer having a thickness ofapproximately 8 μm.

Next, a charge-generating layer is formed as follows. 0.84 g ofpolyvinylbutyral (BX-1, available from SEKISUI CO., Japan) was dissolvedin 17.2 g of ethanol, and then 1.96 g of titanyloxy phthalocyanine(TiOPc, available from H.W. SANDS), as a charge generating material, wasmixed to the solution. This mixture was milled in an attrition millerfor 1 hour. 4.29 g of the resulting milled dispersion was diluted with10.1 g of butylacetate and 0.63 g of ethanol and filtered through asyringe filter having an average pore size of 5 μm to provide a chargegenerating layer coating composition. The coating composition was coatedon the charge transport layer at a speed of 250 mm/min using a ringcoater, thereby forming a charge generating layer having a thickness ofapproximately 0.3 μm.

Then, an overcoat layer is formed as follows. 0.3 g of polyaminoether(Blox 205, Dow Chemical), 0.06 g ofbutyl-9-dicyanomethylenefluorene-4-carboxylate of the following formula,9.7 g of 1-methoxy-2-propanol (Dowanol-PM) were completely dissolved,giving a coating solution. The coating solution was coated using a ringcoater at a speed of 200 mm/min and dried at 120° C. for 20 minutes,thereby obtaining an overcoat layer having a thickness of approximately1 μm.

COMPARATIVE EXAMPLE

An organophotoreceptor was manufactured in the same manner as in Example1 except that 0.3 g of polyaminoether (Blox 205, Dow Chemical) and 9.7 gof 1-methoxy-2-propanol, (Dowanol-PM) were used in preparing theovercoat layer.

The charge potential and the exposure potential of the organicphotoreceptors prepared in Example and Comparative Example were measuredwhile repeating 100 charge-exposure-erase cycles, using a drumphotoreceptor evaluation apparatus (PDT2000, available from QEA). Acorona voltage +8.0 kV was applied to the photoreceptors charged with arelative speed of a charger and the photoreceptor being 100 mm/sec,immediately followed by irradiating monochrome light having a wavelengthof 780 nm at a constant exposure energy of 1 mJ/m². The evaluationresult is shown in Table 1. TABLE 1 Evaluation item Example ComparativeExample Charge potential (V) 552 → 550 537 → 545 Exposure potential (V)103 → 107 112 → 119 E_(1/2) (mJ/m²) 0.327 0.367 E₂₀₀ (mJ/m²) 0.482 0.541*Charge-Exposure-Erase cycling: (1^(st) cycle) → (100^(th) cycle)E_(1/2): Exposure energy required for exposure potential decaying to ahalf charge potentialE₂₀₀: Exposure energy required for exposure energy being 200 V

Referring to Table 1, the overcoat layer prepared in Example 1,containing butyl-9-dicyanomethylenefluorene-4-carboxylate, showed aninitial exposure lower than that of the overcoat layer usingpolyaminoether without butyl-9-dicyanomethylenefluorene-4-carboxylate ofthe Comparative Example. Also, in the overcoat layer of the presentinvention, an increase in exposure potential was not so great incharge-exposure-erase cycling. Further, photosensitivity of the overcoatlayer of the present invention, as expressed by a reciprocal number ofE_(1/2) or E₂₀₀, was greatly increased.

In an electrophotographic imaging process, since the organophotoreceptorcomprising an overcoat layer formed using the overcoat layer formingcomposition can maintain high charge potential and low residual ordischarge potential, the lifetime of the organophotoreceptor can beextended. Also, since the organophotoreceptor according to the presentinvention has good solvent resistance and abrasion resistance, it can beadvantageously used for liquid toner.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A composition for forming an overcoat layer for anorganophotoreceptor comprising: polyaminoether; an electron transportmaterial; and an alcoholic solvent, wherein the polyaminoether isrepresented by the following formula, and is contained in an amount of70 to 99 parts by weight based on 100 parts by weight of the solidcontent of an overcoat layer:

wherein n is an integer from 10 to
 400. 2. The composition of claim 1,wherein the polyaminoether is hydroxylated polyaminoether.
 3. Thecomposition of claim 1, wherein the electron transport material containsan electron transport material represented by the following formula:

wherein A and B are independently one selected from the group consistingof a hydrogen atom, a halogen atom, a C2˜C30 substituted orunsubstituted alkoxycarbonyl group or a C2˜C30 substituted orunsubstituted alkylaminocarbonyl group, and the hydrogen atoms in thebenzene ring is substitutable by a halogen atom.
 4. The composition ofclaim 1, wherein the amount of the electron transport material is in therange of 1 to 30 parts by weight based on 100 parts by weight of thesolid content of an overcoat layer.
 5. The composition of claim 1,wherein the alcoholic solvent is at least one selected from the groupconsisting of 1-methoxy-2-propanol, methanol, ethanol, propanol, butanoland isopropanol, and is contained in an amount of 70 to 99 parts byweight based on 100 parts by weight of the composition for an overcoatlayer.